The FX3U-FLROM-1M is Mitsubishi Electric’s 1 MB flash ROM memory expansion adapter for the MELSEC FX3U compact PLC series, extending the FX3U base unit’s built-in program memory with an additional 1 MB of non-volatile flash storage for program backup, extended data register storage, and file register memory — enabling FX3U applications requiring more device data capacity than the base unit’s internal memory provides, particularly for large recipe systems, extensive production history buffers, and complex multi-product machines where the standard device memory is exhausted. As a left-side special adapter, the FX3U-FLROM-1M connects without consuming extension bus capacity, preserving all 8 right-side extension positions for I/O expansion. Available now at Atlantech Drives with worldwide express delivery and 12-month warranty — complete our quote form for pricing and availability.
What Is the FX3U-FLROM-1M?
The FX3U-FLROM-1M is a MELSEC FX3U series special function adapter module providing 1 MB of flash ROM memory accessible by the FX3U CPU for extended file register storage (R device addresses), extended data register storage (D device addresses beyond the base unit’s standard range), and as a program memory backup medium. The adapter connects to the FX3U base unit’s left-side special adapter interface and appears to the FX3U CPU as an extension of its internal memory space — file registers and data registers stored in the FX3U-FLROM-1M are accessed using standard R and D device addresses in the FX3U ladder program, with no special FROM/TO instructions required. Flash ROM retention is non-volatile without battery backup — data stored in the FX3U-FLROM-1M persists indefinitely across power cycles without the risk of data loss associated with SRAM battery backup, eliminating the maintenance requirement to periodically replace the FX3U base unit’s lithium battery for data retention in critical applications. The 1 MB capacity provides up to 32,000 file register points (R0–R31999), substantially expanding the FX3U’s data storage beyond the base unit’s standard 3,000 file register capacity.
Key Technical Specifications
- Model: FX3U-FLROM-1M
- Memory Type: Flash ROM (non-volatile, no battery required)
- Total Capacity: 1 MB (1,048,576 bytes)
- Connection Interface: FX3U left-side special adapter bus
- Extended File Registers: R0 to R31,999 (32,000 points)
- Data Retention: Non-volatile (no battery backup required)
- Write Endurance: Approximately 100,000 write cycles per flash block
- Program Backup: Yes (complete FX3U program backup to flash ROM)
- Access Method: Standard R/D device addresses in FX3U ladder program
- Current Consumption (adapter bus): 0.06 A at 5 VDC
- Operating Temperature: 0°C to 55°C
- Compatible FX3U base units: All FX3U models
- Weight: Approx. 0.08 kg
Architecture & Design Overview
The FX3U-FLROM-1M implements a flash ROM memory interface that maps directly into the FX3U CPU’s extended device address space, with the adapter’s internal flash controller managing the read/write operations transparently to the CPU program. Flash ROM read operations are single-cycle and do not affect FX3U scan time — reading from R device addresses in flash ROM takes the same time as reading from SRAM data registers. Flash ROM write operations are inherently slower than SRAM writes (flash requires an erase cycle before writing each block), but the FX3U-FLROM-1M implements a write cache that absorbs individual register writes in SRAM and performs bulk flash writes during periods of PLC scan idle time — preventing flash write latency from extending the FX3U scan time under normal operation. The non-volatile write-through architecture means that if power is lost during a data write operation, the previously committed data blocks remain intact and only the in-progress write block may be incomplete — the adapter detects this condition at power-up and completes or abandons the partial write to restore file system integrity. For program backup functionality, the FX3U-FLROM-1M stores a complete copy of the FX3U program and parameters that the CPU reads at power-up if the base unit’s internal RAM program is found to be corrupted — enabling automatic program recovery without GX Works2 intervention in the event of a base unit battery failure causing internal RAM loss.
Expert Tips
When using the FX3U-FLROM-1M for recipe storage in multi-product machines, structure the recipe data in the R device space as a 2D array — recipe number × parameter index — rather than as a flat sequential list. For example, if 100 recipes each have 50 parameters, assign R0–R49 to recipe 1, R50–R99 to recipe 2, and so on — the active recipe is selected by calculating the offset (recipe number × 50) and reading 50 consecutive R registers starting at that offset using a block move instruction (BMOV). This structure enables any recipe to be loaded into the working D register area in a single scan cycle using one BMOV instruction, rather than requiring 50 individual move instructions. For applications that write recipe parameters frequently (multiple times per shift), monitor the write cycle count of the FX3U-FLROM-1M flash memory — the flash ROM has a finite write endurance of approximately 100,000 cycles per memory block. To extend flash memory life, implement a write cache strategy in the FX3U program: accumulate recipe parameter changes in D registers (SRAM) during the production run, and write the accumulated changes to the FX3U-FLROM-1M only at end-of-batch or on operator confirmation — avoiding continuous write cycles that would exhaust the flash memory within months in high-frequency update applications. The FX3U-FLROM-1M’s program backup function is most valuable in environments where the FX3U base unit’s lithium battery may fail between maintenance intervals — in high-temperature environments (above 45°C), the lithium battery life is significantly reduced from the standard 5-year replacement interval, and an unexpected battery failure will cause program loss in the base unit’s SRAM. With the FX3U-FLROM-1M installed and a current program backup written, the FX3U automatically recovers the program from flash ROM at the next power-up after a battery failure.
Frequently Asked Questions
Q: Does the FX3U-FLROM-1M eliminate the need for the FX3U base unit’s lithium battery?
A: The FX3U-FLROM-1M eliminates the need for the battery to retain program data and R device file register data — both are stored in non-volatile flash ROM. However, the FX3U base unit’s battery still provides backup power for the real-time clock (RTC) and for SRAM-based D data registers (D0–D7999 standard range) that are not stored in the FX3U-FLROM-1M. For applications where D register data loss on power failure is acceptable, the battery maintenance interval can be extended; for applications where D register data must survive power loss, the battery remains necessary or a second layer of SRAM-to-flash backup logic should be implemented in the FX3U ladder program.
Q: Can the FX3U-FLROM-1M be used simultaneously with the FX3U-CF-ADP CompactFlash adapter?
A: Yes. Both adapters connect to the FX3U left-side adapter interface and can coexist on the same base unit, occupying two of the four available adapter positions. The FX3U-FLROM-1M provides non-volatile internal storage for program backup and static recipe data, while the FX3U-CF-ADP provides removable card storage for dynamic production data logging and batch record keeping — the two adapters complement each other for comprehensive data management in complex production applications.
Q: How is the program backup to FX3U-FLROM-1M initiated?
A: Program backup from the FX3U internal memory to the FX3U-FLROM-1M is initiated using the dedicated FMWRITE instruction in the FX3U ladder program, or via the GX Works2 PLC Memory operation interface while connected to the FX3U via USB or RS-422. Automatic backup at power-up (copying the program from flash ROM to internal SRAM) occurs automatically if the FLROM-1M contains a valid backup and the base unit’s internal SRAM program is detected as corrupted — no programming or operator action is required for the automatic recovery sequence.
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